Numerical analysis on a four-stage looped thermoacoustic Stirling power generator for low temperature waste heat

Abstract

Recent developments in thermoacoustic technologies have demonstrated that multi-stage looped thermoacoustic Stirling engine would be a promising option for harvesting waste heat. Previous studies on multi-stage looped thermoacoustic systems were mainly focused on heat-driven refrigeration or heat pumping, while much fewer work were done on power generations, especially those for recovering low temperature heat. In this work, a four-stage looped thermoacoustic Stirling power generator for generating electricity from low temperature waste heat at 300°C is systematically studied. A numerical model is built and then validated on an experimental four-stage looped thermoacoustic Stirling engine. On the basis of the validated model, the effects of the coupling position for the linear alternators and the regenerator position on the acoustic characteristics and performances of the power generation system are numerically investigated. The distributions of the acoustic fields along the loop, including the pressure amplitude, volume flow rate, phase angle, specific acoustic impedance and acoustic power, are presented and analysed for three representative coupling modes. Superior efficiency is achieved when the linear alternators are coupled near the cold ends of the thermoacoustic cores on the resonators, while more electric power is generated at the hot ends. The worst performance is expected when the linear alternators are connected at the middle of the resonators. The underling mechanisms are further explained detailedly by analysing the characteristics of the acoustic fields and output acoustic impedances for different coupling modes. Furthermore, the regenerator position in the thermoacoustic cores is found to have a remarkable influence on the output electric power, while it is less important for the efficiency. The optimized four-stage looped thermoacoustic Stirling power generator is able to provide a maximum electric power of 1223W with a highest relative Carnot efficiency of around 0.20. This work provides in-depth insights into the operation principle of the looped thermoacoustic Stirling power generator and will be helpful for future developments of similar waste heat recovery systems.